Washington  - Discovery astronauts were preparing to undock from the space station later Wednesday to head back to Earth after completing a milestone mission that has doubled the station's capacity.

The mission astronauts installed the fourth and final set of solar panels needed to double power capacity at the station so it can hold six instead of the current three long-term residents - possibly as early as May.

But controversy has emerged over the naming of a new room at the International Space Station that will provide extra space for the expanded long-term crew.

The name contest applied to Node 3, a cupola to be delivered in February 2010 that will offer astronauts an "unrivaled" panoramic view of Earth and space. The cupola will also house the control station for the station's giant robotic arm.

Thinking to engage the public in the naming process, NASA invited people to vote on names for the room on its website. It had an epic identity in mind, such as Serenity or Legacy.

But the US space agency also invited write-ins, and was surprised to find the top vote-getter was none other than TV comedian and political satirist Stephen Colbert.

Colbert, star of The Colbert Report on the cable channel Comedy Central, suggested to his fans that they rush to the website and cast their votes.

The Colbert name won, according to the Houston Chronicle, but it wasn't yet known whether NASA would honour the write-in campaign.

In the contest rules, NASA says it will consider the voting results, but would not be bound by them. "NASA reserves the right to ultimately select a name in accordance with the best interests" of the programme, it said.

In fact, the website indicates that one of its preferred names, Serenity, was in the running to win the contest.

Other popular names in the write-in were Gaia, the earth goddess; Xenu, a character in Scientology mythology who was dictator of a "Galactic Confederacy" who brought human beings to Earth 75 million years ago; and Ubuntu, the spirit of reconciliation anchored in the Bantu languages of southern Africa.

When Discovery departs, it will leave behind Japanese astronaut Koichi Wakata, the first astronaut from his country to take up long- term residence in the orbiting station.

His predecessor on the ISS crew, US astronaut Sandra Magnus, will return home with the Discovery, which is set to land in Florida on Saturday. (dpa)